1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to a method of generating data and transmitting a synchronization channel in a multicarrier multiple access communication system.
2. Discussion of the Related Art
FIG. 1 is a diagram for a method of generating a signal in a transmitting side using multicarrier according to a related art.
Referring to FIG. 1, an input data sequence, {right arrow over (d)}=[d0, d1, . . . , dN-1]T, includes N data. The input data sequence is converted to a plurality of parallel data sequences via a serial-to-parallel converting unit 100. Generally, the serial-to-parallel converting unit determines how many parallel data sequences will be generated from an input data sequence by interoperating with subcarrier modulating units 110-0 to 110-k of a following inverse fast Fourier transform (hereinafter abbreviated IFFT) unit 105. In the following description, assume that a fast input data sequence is converted to k slow parallel data sequences by the serial-to-parallel converting unit 100.
The IFFT unit 105 loads mutually different subcarriers on the k slow parallel data sequences inputted to the IFFT unit 105 (i.e., subcarrier modulation) and then generates a serial IFFT transformed input data sequence using the following parallel-to-serial converting unit 110. Afterwards, the IFFT transformed input data sequence is transmitted to a receiving side via a radio frequency (RF) unit 130. In case of such a multicarrier transmission scheme as an orthogonal frequency division multiplexing (hereinafter abbreviated OFDM) scheme, the IFFT unit 105 arranges k subcarriers 110-0 to 110-k respectively allocated to k parallel data sequences in a manner that the k subcarriers are orthogonal to each other on a frequency axis, whereby frequency division is achieved to avoid inter-subcarrier interference.
Generally, in a digital communication system, an input data sequence is constructed as combination of 1 and 0 and has an on/off pattern of each rectangular wave in a time domain. If Fourier transform is performed on a square wave, it can be represented as a sum of integer-fold frequency components. In particular, data representation in time domain is represented as data in frequency domain. In more particular, random digital data is represented in time domain and can be also represented in corresponding frequency domain. For details, a process for generating a multicarrier signal shown in FIG. 1 is described as follows.
First of all, if the IFFT unit 120 shown in FIG. 1 performs a procedure (i.e., subcarrier modulation) of a subcarrier having a mutually different frequency corresponding to each parallel data sequence by the corresponding parallel data sequence, a frequency of the corresponding parallel data sequence is increased by a frequency of the multiplied subcarrier in viewpoint of frequency domain. Each parallel data sequence modulated with the corresponding subcarrier enters the parallel-to-serial converting unit 105 to be represented as an input data sequence in the IFFT transformed time domain.
Formula 1 shows an input data sequence via N-size IFFT.{right arrow over (s)}=[s0, s1, . . . , sN-1]T=F−1{right arrow over (d)}  [Formula 1]
In Formula 2, ‘F−1’ indicates an inverse Fourier transform matrix. And, the IFFT transformed input data sequence is named a multicarrier symbol. Moreover, a cyclic prefix (hereinafter abbreviated CP) can be inserted in the multicarrier symbol. The CP is formed in a manner of copying a predetermined portion of a rear part of a multicarrier and then adding the copied portion to a front part of the corresponding multicarrier symbol. Before primary data of the multicarrier symbol arrives at a receiving side, the CP eliminates influence attributed to a multipath of the received multicarrier symbol. In order to add a CP to a multicarrier symbol, a CP adding unit (not shown in FIG. 1) can be added to the IFFT unit 120. For reference, in case of using an OFDM transmission scheme as a multicarrier transmission scheme for example, frequencies of the subcarriers shown in FIG. 1 are mutually orthogonal to each other and parallel data sequences modulated with the subcarriers are mutually orthogonal to each other in frequency domain.
In the following description, a procedure for acquiring synchronization of a mobile station in a mobile communication system is described.
First of all, in order to communicate with a base station, a mobile station in a mobile communication system receives a synchronization channel (SCH) in the first place and then performs synchronization acquisition and cell search for smooth data transmission and reception with the base station using information carried on the synchronization channel (SCH).
A mobile station acquires synchronization from a base station and obtains a cell ID of a cell to which the mobile station belongs. This procedure is called a cell search. The cell search is classified into an initial cell search and a neighbor cell search. In this case, the initial cell search is performed when a mobile station initially turns on power. And, the neighbor cell search means that a connected mobile station or a mobile station in idle mode searches for a neighbor base station. In a mobile communication system, a system configuration is generally implemented based on a cell. In order to access a mobile communication service, a mobile station at a specific location matches synchronization with a base station of which signal is received with highest strength due to signal characteristics (i.e., a mobile station acquires synchronization). For this, a base station transmits a signal on a synchronization channel to enable mobile stations within a range of the base station to acquire synchronization from synchronization information of the base station. Once the mobile station matches synchronization with the base station, the mobile station is able to obtain various kinds of control informations from the base station. Afterwards, the mobile station informs the base station off a presence of the corresponding mobile station using such a means for matching uplink synchronization as a random access channel (hereinafter abbreviated RACH) and then tries a call connection with the base station. The synchronization channel is explained in detail as follows.
First of all, a synchronization channel is used for a mobile station to acquire time synchronization and frequency synchronization with a base station in the early stage of access. The synchronization channel is used for the mobile station to obtain a cell ID of the base station and additional control information in accordance with the acquired and detected time and frequency synchronizations. Thus, a process for a mobile station to acquire or obtain time and frequency synchronizations with a base station, a cell ID of the base station and relevant additional control information is performed via a synchronization channel. And, a synchronization acquiring process of a mobile station can be mainly divided into a step of acquiring frequency synchronization, a step of acquiring time synchronization, and a step of obtaining a cell ID of a base station.
In particular, a mobile station performs a step of performing frequency offset estimation and compensation for time and frequency synchronizations with a base station using a synchronization channel transmitted from the base station and then performs a step of obtaining a cell ID of the base station. In more particular, the cell ID obtaining step includes the steps of performing frame synchronization by searching a cyclic prefix (CP) of a transmission frame of a physical channel carrying the synchronization channel and obtaining a cell group ID and cell ID included in the synchronization channel. If necessary, the cell ID obtaining step can further include the steps of searching an antenna configuration included in the synchronization channel and searching a downlink (DL) frequency hopping indication which is one example of frequency configuration information.
Moreover, the mobile station is able to recheck the cell ID obtained in the previous step using such a reference signal as a DL pilot signal transmitted from the base station for more accurate cell ID security in performing a cell search.
However, as mentioned in the foregoing description, a synchronization acquisition of a mobile station needs a multi-step acquiring procedure. For this, a synchronization channel needs to be subdivided to fit the respective the steps. Specifically, in consideration of a processing by a multicarrier symbol unit in case of a mobile communication system using a multicarrier, the subdivided synchronization channel needs to be allocated to a minim radio resource region.